In situ combustion method for residualoil recovery from petroleum deposits



tion of preferred flowing United States Patent O D 12 Claims. (Cl.166-11) The present invention relates to a method for recoveringresidual oil from petroleum deposits.

This application is a continuation-impart of application Ser. No.440,852, filed Mar. 18, 1965, and applicant relies upon the disclosureand requests the filing date and all rights and priorities claimedtherein.

The disclosure of application Ser. N-o. 215,493, filed Aug. 6, 1962, nowU.S. Patent No. 3,276,518, and assigned to the assignee of ythe presentinvention is incorporated by reference into the disclosure of thepresent invention.

It is an object of the present invention to provide an improved methodfor the -recovery of residual oil remaining in partially exploited oilfields.

It is another object of the invention to provide an improved method ofin situ combustion for the exploitation of bitumens from petroleumdeposits.

Another object of the present invention is to provide a method of oilfield exploitation comprising flooding the field with water in thedirection of exploitation while conducting an in situ combustion in adirection perpendicular to the direction of exploitation.

Other objects of the invention are the pretreatment of oil fields priorto exploitation by the circulation of flood water containing salts andcatalysts.

Still further objects of the invention are the use of compressedactivated gases of combus-tion for the in situ combustion withcontrolled pressure variation of the combustion gases.

According to the pri-or art, when the production or recovery from apetroleum reservoir or deposit has become uneco-nomical, secondaryrecovery practices are initiated in order to recoverat leastpartiallythe still adhering proportions of hydrocarbons. The quantitiesinvolved amount on the average to 40 to 60% of the original content ofthe petroleum deposit.

Frequently employed prior art techniques for the secondary recoveryeffect an increase -of the pressure or of the temperature of the depositor reservoir. For example, in the gas-drive methods, partially withlight hydrocarbons, and when flooding with water from injection holes,the pressure of the deposit is displaced toward recovery holes. Such aprior art process is disclosed in British Patent No. 726,712. Thesesteps are, however, only partially successful; preferred channels aregenerally formed and the oil of the deposit sections positioned betweenthe drilled holes is hardly affected thereby.

For the purpose of increasing the tempera-ture of the deposit, hot wateror vapor injections are carried out. In this prior art method, however,the danger of the formapat-hs directly to the recovery lholes isparticularly great so that the media being introducedbeing used in partonly to a very small extentare prematurely lifted or brought out again.For the purpose of increasing the deposit temperature an in situcombustion is also used. According to this method, the con-tent of thedeposit is partially evaporated and partially rendered more readilyflowable by means of a partial combustion. In the process of the directlinear flow path or passage from compression holes to adjacent recoveryholes, a cylindrical burnt-out rock structure will `be formed in thedeposit or reservoir in the course of the continuous supply of oxidationagents. From the compression holes to the recovery holes this rockstructure will constantly increase and be lengthened, and eX- te-nd fromthe compression hole with a forwardly positioned gas-permeable tongueinto the recovery hole. The axis of the combustion front extends fromthe compression hole to the recovery hole. In case the deposit is filledwith liquid, this direction of the axis is predetermined by virtue ofthe fact that free-blowing thereof is required prior to beginning the insitu combustion, and the liquid will be rising to the upper edge of thedeposit at the recovery hole. The oxidation tagents flow on this axisbehind the combustion front in the burnt-out rock of the deposit. Aheadof the combustion front the `resultant inert combustion gases flow mostrapidly, while at the casing of the burnt-out rock structure theoxidation agents will also flow in the direction of the axis, but moreslowly due to the longer flowing path thereof. At the casing of theburnt-out rock structure the disturbing factor arises that resultantoxygen-poor combustion gases flowing laminarly in the rock of thedeposit keep further oxidation agents almost entirely away from thesurface of the casing, thus allowing oxidation agents to becomeeffective at best only in a greater dilution so that at a large distancefrom the axis of flow coke particles are deposited, due to the existingheat, in this cylindrical casing and will no longer be burned because ofthe insufficient amount of oxygen. This behavior at the casing of therock structure and the intensified flow in the vicinity of the axisresult, for an oil field during exploitation at these surfaces, in areduced action in both the horizontal and in .the vertical directionbetween the adjacent holes and the overlying rocks. The coke depositsrender it diflicult to keep all of the flowing paths free and localincreases of pressure may be produced in the deposit and often lead toundesirable flowing directions, thus guiding the combustion forcibly toother paths. These disturbing operational conditions have the resultthat vast parts of the reservoir or deposit remain unexploited.

According Ito the present invention, rows of recovery boreholes defininga recovery Zone, rows of treatment and leading boreholes defining atreatment zone, and rows of flooding boreholes are drilled in an oil eldfor the recovery of residual oil therein. The direction of flow of theproduct to be recovered is controlled by the pressure gradient from theflooding boreholes to the recovery boreholes. The product beingrecovered is treated in the treatment zone by controlled in situcombustion in a direction perpendicular to the direction of flow.

-Other objects and advantages of the present invention will be apparentupon reference -to lthe accompanying drawings which schematicallyillustrate the manner in which the present process is carried out.

In the drawing a top plan view of a portion of an underground deposit ofliquid bitumens is schematically illus-trated. A flooding zone, atreatment zone, and a recovery zone are illustrated with the respectiveflooding boreholes, treating and leading boreholes, and recoveryboreholes therein. The sections of the drawing shown in Roman numeralsillustrate the process steps of the invention conducted between the-treating boreholes and leading boreholes perpendicular to the directionof flow of the recovery.

A method has ibeen proposed to provide a more complete recovery of thecontents of a petroleum deposit or reservoir by means of the in situcombustion -by opening an oil field with staggered rows of boreholeswhich serve as flooding boreholes in a structurally deep zone and asrecovery boreholes in a structurally high zone. Arranged between theserows of boreholes are so-called treating boreholes an so-called leadingboreholes in one treatment zone in which the content of the deposit isheated and loved in a circulation pattern by virtue of the fact tha-t itrecovered from the leading boreholes above ground nd reintroduced, afterheating, into the deposit through 1e treating boreholes. Heating iseffected in that hot iodied and activated combustion gas is admixedabove round to the liquid content of the deposit. The modied combustiongas which contains little nitrogen is prouced by burning predominantlygaseous deposit con- :nt with air enriched with oxygen from 8O to 95% inhe pressure combustion chamber of a boiler. By admixng enriched oxygencontaining, in addition to 80-95% txygen, also a residue of yfrom to 20%nitrogen, an .acti- 'ated combustion gas is recovered from the modifiedcomustion gas. The treating -boreholes and the leading boreloles of onetreatment zone are staggered and therefore tre arranged that themovement of the circulation takes )lace in a direction which differsfrom the flow lmovement `esulti'ng from the primary movement from theflooding )orehole to the recovery borehole. With the activatedaombustion gas, an in situ combustion is initiated in the reatcd depositand a reaction zone is created in the treatnent zone. As a result of thecombustion of petroleum leposit -or reservoir -contents in the depositor reservoir with the oxygen, modified combustion gas is produced whichhas the property of condensing and, respectively, 3f becoming dissolved-in the liquid deposit content with- Jut leaving a Igaseous phase.

It has now been found that for purposes of exploiting 1 deposit orreservoir by means of in situ combustion, other factors have to be takeninto account if as complete as possible a recovery is to be achieved.The use of the linear flow 4between compression hole and the recoveryhole not only involves the hazard of burning channels and thus a greatloss because of untreated deposit portions, but the combustion procedureitself is an unstable process if the combustion gases iiow in thedirection of the axis between the compression hole and the recoveryhole. If the temperature is too high, a strong cracking Will occur inthe content of the deposit and, .in turn, produce a high coke portion sothat the burning progress or advance becomes smaller and thus thecombustion ternperature is further increased. The further growing cokeportion or constituent may, in places, become so high that obstacles :inthe iiow movement will set in additionally also in the combustion frontwhich may lead to local obstructions. In this in situ combustionprocess, the advance or progress of the combustion cannot beaccelerated.

In order to be able to control this process and to stabilize the same,while simultaneously also avoiding the burning of channels, measures arethus required which render it possible to influence the reactiontemperature `and the reaction direction in a regulating manner. Theabove-mentioned method for the in situ combustion in a separate reactionzone being positioned between a flooding borehole and a recoveryborehole whose burning direction differs from the primary movement whichresults from a pressure gradient from the flooding borehole to therecovery borehole is suitable therefore if it is combined with aiiooding that is carried out in a specific manner.

The in situ combustion according to the method of the presentapplication in combination with a flooding is automatically stabilizedin lthe following manner. Deposit proportions or portions which arepresent predominantly in solid form as coke are burned in the reactionzone during the in :situ combustion. This solid fuel is formed duringcracking in the residue from a flash evaporation by means of hot gasesand vapors from the react-ion zone and is a process which corresponds toa process for the treatment of petroleum which has been called delayedcoking. If the temperature in the reaction zone is very high in thepresence of many solid coke proportions or constituents, the depositrock is heated to a high temperature. The flood water owing in directlybehind the traveling reaction or combustion front will form at this rocklarge amounts of highly heated vapor. The heated vapor effects insections lying ahead of the combustion front, an intensified iiashevaporation of the liquid petroleum so that only small quantities ofsolid coke portions are left over and after subsequent combustion lesshigh temperatures arise. With these lower temperatures, the rock isheated to not quite as high a temperature. Less vapor is produced atthis lower temperature rock which, accordingly, will effect a lower Hashevaporation so that from the ash evaporation large amounts of heavyliquid hydrocarbons will again remain behind. As a result, in thedelayed coking a larger amount lof lcoke will lbe deposited as solidfuel in the =re action zone. The gaseous and vaporous cracking productsare mixed with the modified combustion gas and the resultant watervapor, so that the procedure and events described hereinabove arerepeated. The in situ combustion in the react-ion zone is carried outwith activated combustion gas consisting of carbon dioxide, water vaporand larger amounts of enriched oxygen. Mixed therewith is the additionalvapor, formed at the hot rock, in the reaction zone and increases theendothermic water vapor reduction which additionally keep thetemperature peaks low. The reaction temperature will thus folilow acourse in an undulatory manner about a mean Value as a result of whichfact the combustion process becomes stabilized since it cannot increasebeyond control nor cause itself to be spent.

According to the present invention iiood water is introduced underpressure through flooding boreholes behind the reaction zone and guidedin the direction of the primary movement from the iiood zone to therecovery zone. Additional amounts of vapor resulting from contact withthe hot burntout rock `are compressed by a pressure gradientcorresponding to the primary movement through the reaction zone at antangle to the axis perpendicular thereto. Limited amounts of ana-ctivated combustion gas having increased oxygen content for thepurpose of attaining high combustion temperature are introduced in thecombustion zone -with a liow perpendicular to the primary movement andtherewith a delayed coking is carried out with the residues still beingpresent in the reaction zone. Thereupon a strong flash evaporation `ofthe hydrocarbons is effected with the resultant hot modified combustiongas together with the equally strongly heated water vapors ahead of thereaction zone so that only small amounts of residue will remain for -asubsequent Adelayed coking during the advance movement of the reactionzone. All the vapors and gases from the flash evaporation condense incolder sections of the petroleum deposit positioned before the reactionzone or are possibly `recovered through recovery holes positioned at thereaction zone.

Accordingly, it is important that the flood zone follow the movingreaction zone which is displaced, due to the pressure gradient of theprimary movement, parallel to the axis of the combustion direction.Corresponding to the advance of the flooding water, additional amountsof water vapor are formed at the hot burnt-out rock, which has been leftbehind by the moving reaction zone, and will tiow into the reaction zonepositioned thereahead. The pressure gradient -in the primary movementand the `direction of flow of the resultant water vapor force alsomiiuence the activated combustion gas having been introduced into thisdirection of flow. The oxidation agent is thus forced to always flowinto the deposited coke from the delayed coking so that marginalproblems or burntout rock structures cannot be formed or be produced.The water vapor with the formation of water gas acts in this care in atemperature-regulating or controlling manner; the major portion isconverted into over-heated vapor which latter, after iiowing through thereaction zone being disposed at right angles to the direction of itsiiow, will bring about a iiash evaporation of the deposit or reservoircontent ahead of the reaction zone. The regulation or control of theportions to be burned in the reaction zone as well as the regulation ofthe reaction temperature renders it possible to use an activatedcombustion gas having an increased content of enriched oxygen (thequantity thereof may be increased up to a portion of 40% in thecombustion gas). lIf such a reactive gas were used for the in situcombustion without the combination with water vapor, the consequencesreferred to and enumerated hereinabove would be inevitable.

During the condensation of the water vapor in the colder parts of thedeposit or revervoir, considerable amounts of electrolyte-free water areproduced, which may cause swelling of the clay-containing orargillaceous constituents of the reservoir rock, particularly indeposits having a low content of salt-bearing adhering water. Thepermeability is thus impaired to a more or less considerable degree andthe path of the combustion gases and of the combustion front isunfavorably influenced.

It has, therefore, been proposed that, prior to initiating the in situcombustion, ilood water being charged with salt and/or catalysts becirculated between the treating boreholes and the leading boreholes.With this ilood water, a salt enrichment in the treatment zone isachieved so that swelling by condensate water of the subsequent in situcombustion is prevented. This accentuation or increase of the salinityis particularly important if the combustion is carried out with enrichedoxygen since at that time an intensive combustion at high temperaturetakes place so that aside from the reaction water also a great amount ofevaporated adhering water will reach forwardly positioned coldersections.

The catalysts which are deposited possibly at the same time as the saltmay become effective once the reaction zone has penetrated into therespective section or compartment of the deposit or reservoir. They mayserve for influencing the cracking, coking or combustion of the depositcontent and, respectively, support the same.

In order to render the production of or recovery from a petroleumdeposit or reservoir independent of the respective conditions prevailingtherein and in order to make the recovery as complete as possible, theprocess is carried out as follows, with particular reference given tothe drawing of the invention.

The starting point or basis is the process or method .known in the artof opening a field by flood boreholes and recovery boreholes betweenwhich treating boreholes and leading boreholes are disposed. An in situcombustion is initiated from the treating borehole to the leadingborehole and a reaction zone is thus created having a movement of flowdiffering from the primary movement from the flooding borehole to therecovery borehole. As is shown in the drawing, the iield to be recoveredis subdivided into individual sections extending at right angles to theprimary movement and being delimited by rows of boreholes or wells inthe direction of the primary movement. In the same direction, the fieldto be recovered is subdivided into flood zone, a treatment zone, and arecovery zone. Disposed in the treatment zone are two boreholes whichdelimit the section laterally, namely as treating boreholes BB and asleading boreholes LB. Content from the deposit is recovered from theleading boreholes LB aboveground and there subjected to a treatment, asindicated at A in section I. This treatment consists of a heatingoperation by admixing hot combustion gases which are completely solublein the deposit content and, respectively, are condensable thereinwithout leaving a gaseous phase. These gases defined as modifiedcombustion gas, consist of carbon dioxide, water vapor and some nitrogenand may be recovered by burning hydrocarbons with an oxidation agent,predominantly air, containing only a little nitrogen. The treatment may,moreover, consist also in a separation of the deposit or reservoircontent being removed from the leading borehole into liquid and gaseousportions, at which time the 4liquid constituents are separated asrecovered product and the gaseous portions serve for producing themodified combustion gas. The treated and, respectively, convertedproduct is introduced once again under pressure into the deposit throughthe treating borehole BB. Due to the fact that the medium is compressedinto the treating borehole and that the discharge or removal is effectedthrough the leading borehole, a forced flow is produced under theinfluence of the pressure gradient between these two boreholes in thedeposit or reservoir. After the circulation with the forced flow andheating of the deposit section has been carried out for some time, anenriched oxygen containing aside from to 90% of oxygen additionally alsofrom 5 to 15% of nitrogen is admixed to the medium aboveground, as shownat B in section III of the drawing, and an activated combustion gas isthus formed. With the latter, an in situ combustion is initiated in thedeposit and a reaction or combustion front is produced whose axis is atright angles to the primary movement resulting from the pressuregradient ahead of the flooding zone to the recovery zone. Accordingly,the reaction Zone in which the in situ combustion is carried out islaterally delimited by the leading borehole and the treating borehole.

In order to include and entrain further parts of the deposit orreservoir section being delimited by the two boreholes into the range ofaction of the reaction Zone, a pressure gradient is produced in thedirection of the primary movement to thus effect a parallel displacementof the reaction zone in the direction toward the recovery zone. Thetraveling speed or speed of 'movement thereof depends upon the oxygencontent of the activated cornlbustion gas supplying the combustion inthe reaction zone and upon the amount of fuel being formed in thereaction zone and is controlled by the amount of oxygen. The progress oradvance of the combustion is always slower than the speed of flow of thegases and vapors. The pressure gradient is built up Iby compressing theflood water into the flooding boreholes and by recovering depositcontent from the recovery boreholes. The flood water line follows thereaction zone and ilows into the burnt-out hot rock. While water vaporsare formed, the recovery of the heat being stored there taires place andthe vapor acts in a regulating manner on the combustion process in themanner described hereinabove. The: reaction zone is thereby displaced ina direction toward the recovery zone, as illustrated in sections V andVII of the drawing.

In the stage illustrated at sections V and VII, activated combustion gasmay be introduced both into the treating borehole and into the leadingborehole of the deposit in order to supply the traveling or movingreaction front with this mediu-m. When the reaction zone has traveled,for example, half the distance to the next row of boreholes, a largeheat source will have been produced in many instances ahead of andbehind the reaction zone which is sufficient to assure that the secondhalf to the next row of wells is now de-oiled by flooding only so thatfor this operational section additional oxygen is no longer requiredsince the ilood water will drive the heat being introduced ahead of it.If, however, in unfavorable deposits or reservoirs with the contentthereof the traveling reaction front comes into the area or region ofthe next row of boreholes in the direction toward the recovery zone,these boreholes will assume the function of the leading and,respectively, treating boreholes and the boreholes left behind will thenserve as flooding boreholes. The flood water being introducedtherethrough is converted into vapor on the still hot rock of theburnt-out deposit section and this vapor will fulfill the abovedescribedimportant functions in the course of the process.

Furthermorenin the case of highly viscous deposit content or in the caseof a low permeability of the reservoir rock, flood water being chargedwith oxygen is compressed into the flooding borehole and the supply ofac-` tivated combustion gas to the reaction zone is discontinued whenapproximately half of the -distance between two parallel rows ofboreholes has been burnt out by the reaction zone travelingtherebetween. The oxygen con- :nt of the flood water is so chosen thatit willsuice to iaintain a weak combustion since the latter will takelace only in the preheated deposit or reservoir rock. `he process ormethod modification may be carried out ieriodically, possibly until thenext row of boreholes has leen reached. This stage of the method isillustrated in ection IX of the drawing.

The process steps illustrated in sections I, III, V, VII ind IX of thedrawing have been shown in separately aositioned sections side-by-sideonly for reasons of greater zlarity. They take place, of course,successively in each `ection.

It has been found to be expedient not to take all of he sections beingpositioned side-by-side into treatment 1nd production at the same time,but to separate simul- ,aneously treated sections by inter-posedsections. The Jegi'nning of the treatment in these intermediate sectionsnay .be effected at different time periods, for example, if ln the firstsections no treatment above ground is required and the oxygenrequirement is reduced. It may, however, also be started only after thefirst sections have been redered empty by recovery. In this particularmode of carrying out the method, the requirement with respect todevices, such as pumps, compressors, boilers and oxygen plants, may bekept smaller than is the case if simultaneously the entire deposit fieldis opened up. Since the combination of the in situ combustion with waterfiooding a deposit or reservoir can be exploited more rapidly and morecompletely than in the practices and techniques of the prior art, theeconomical success is also considerable. On the average, only half ofthe deposit surface needs to be treated with oxygen.

As has been pointed out, it is of importance for the purpose ofrecovering the deposit or reservoir content as completely as possible toinfluence and to guide apart from the forced flow in the reaction zonealso the directions of flooding in the ooding range. This may beachieved, for example, in that individual ooding boreholes or treatingor leading boreholes which have become flooding boreholes are suppliedtemporarily with different and varying amounts of ood water, or thatspecific lboreholes are temporarily closed off completely. It is alsopossible to move flood water in a circuit between neighboring boreholes.With all of these modifications, intersecting and traversing flows, owdirectional and pressure changes or reversals are attained, theformation of preferred channels and small narrow channels is renderedimpossible and, in this manner, the entire content of a reservoir ordeposit is put into motion and lifted out.

In order to be able to carry out the recovery of an extensive depositfield with greater distances of the boreholes of, for example, 30()meters, it has `been found to be advantageous to modify the methoddescribed herein in the following manner. Activated combustion gas iscompressed into a atreatment zone delimited by a treating borehole and aleading borehole, and specifically into one of the two boreholes in aperiodically changing sequence, and the other borehole is then closed.The movement of flow of the water vapor flowing vertically through thecombustion zone is maintained at that time. The two movements of flowact upon one another in the form of displacement bodies which areinuenced by the pressure gradient (from the compressed borehole to theclosed-off borehole) and by the viscosity gradient (from the comhusiongas to the water vapor having considerably lower viscosity). A conicaldisplacement of the range of action of the activated combustion gastakes place thereby, with a broad base of the cone in the region of thehigh pressure of the combustion gas around the compressed borehole andwith the apex in the range of the lower pressure where the borehole isclosed. The

predominance of the activated combustion gas at the base results in anintensified cracking, the reduction thereof at the apex of the coneresults in an intensified flash evaporation of the deposit content. Dueto the periodic change of the compressed borehole, and, respectively, ofthe closed borehole, the cone-shaped range of action is, in each case,reversed. The result thereof is the desired ,guiding or control of thereaction process-even in case of a larger distance between thelboreholes--and a favorable utilization of the vapor produced in thedeposit or reservoir.

There exists the danger, however, that after a prolonged period of timeof operation -only few combustible residues will remain in the vicinityof the compressed borehole. In order to prevent and counteract this, afurther process step is proposed which consists in lthat, during thereversal of the direction of ow, liquid or gaseous hydrocarbons,possibly together with modified combustion gas, are introduced into theheretofore closed borehole for a short time. The hydrocrabons may be ledor branched off from the products of the recovery boreholes or fromother boreholes which are in a different period or phase of the processat that particular time. They serve for renewing and, respectively,complementing the supply of combustible media in the zone or area of theborehole. Thereafter oxygen is supplied by compressing activatedcombustion gas into the borehole and the combustion front is therebyfurther kept in motion, or possibly, also newly ignited.

If a deposit or reservoir contains a borehole-permeable reservoir rock,or if the deposit content is thinly liquid and easily movable, it may beadvantageous to carry rout the two process steps of the in situcombustion and of the flooding separately and successively, rather thansimultaneously. A combustion zone is initially built up in the treatmentzone of a deposit or reservoir and guided in a forced flow byintroducing oxidation agents between the Itreating borehole and theleading borehole. After stopping the forced flow between the twoboreholes, a ooding of the treatment zone is subsequently initiated andcarried out at an angle differing from the direction of the forced fiowof the combustion and which is enhanced by taking up the recovery in thedirection of the primary movement. The heat which is produced in thecombustion zone is sufficient to Iflood out the deposit con-tent to thenext row of boreholes.

When a deposit or reservoir field reaches the end stages of the recoverythereof, compressed air together with flood water is compressed into thefiooding boreholes. The field is thus charged with a supply of pneumaticenergy which is sufficient to keep up the recovery over a period of timewhich may be considerable, under certain circumstances, and withoutadditionally requiring the use of the conventional devices and meanswhich are thus free to be employed in a different place at an earlierperiod of time.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative of.the remainder of the specification and claims in any way whatsoever. 60

Example In a 15 meter thick deposit located l250meters underground an insitu combustion and flooding was performed in accordance with thisprocess. This stratum is under a pressure of atm. at 60 C. It has aporous volume of 26% by volume, filled with mineral oil, natural gas andnatural water. In a section of this stratum a burning front is formedbetween a leading borehole and a treating borehole and extendingtransversely to the primary pressure gradient from the flooding boringsto the recovery borings. The burning front is maintained by theintroduction of 35.6 Nm.3 (cubic meters `at normal conditions ofpressure and temperature) oxygen mixed with steam and carbon dioxide perm.3 of the rock that is contained in the burning front. This amount ofoxygen burns 17.15 kg. carbon and hydrocarbons per m of the deposit,thereby liberating 146,000 kcal. T-he latent heat of the hot mixture ofsteam and CO2 contains a total of 151,400 kcal. of heat energy per m.3of the deposit. In the burning front a temperature of, e.g. 480 C.reached. In the completely burnt-out rock which remains behind theburning front during its advance in the direction of the pressu-regradient, there is contained at this temperature 195,000 kcal. of heatenergy per m of the deposit. This amount of heat energy was produced inpart by the heat of combustion per m.3 of deposit, and also in part bythe steam and gases of combustion which were heated by the previouslyburnt-out rock.

The process is contained as follows:

The flooding water advance into the rock which has been burned empty andis there vaporized and forms per m.3 of the deposit 166 kg. steam underthe pressure in the stratum. The steam then forces its way through theburning front where it is further superheated. From the hot rock 133,000kcal. per m.3 of heat energy are thus recovered, w-hile in the burnt-outrock at 200 C., 62,000 kcal. per m.3 remain behind. The heat losstherefore amounts to 40.8%. However, by a further utilization of thisresidual heat for subsequent warming of more of the flooding water in aregion of lower temperature, another 20,000 kcal. are recovered so thatthe loss of heat in the rock is further diminished by about or down to27.5% with only 42,000 kcal. remaining in the stratum. Further heatlosses occur as the result of convection. In a deposit 15 m. thick, theloss by convection from the two base surfaces with a total area of 2 m2is 49,300 kcal. In relation to the introduced or generated heat, thisrepresents a heat loss of 32.8%. The total loss of heat per m of theburnt-out rock during this process is therefore 60.3% of the heatintroduced or generated.

The excess of heat energy remaining in the stratum is thereforel51,4009l,300=60,100 kcal. per m of the deposit. This retained heat inconjunction with the pressure drop ahead of the burning front convertssome of the flooding water into steam which in turn heats the stratumcontents that are encountered by the steam. This considerable excess ofheat energy is sufllcient to vaporize the hydrocarbons which fill halfthe distance between two rows of borings as viewed in the primarydirection. It is, therefore, not necessary to keep a burning front, inoperation over the entire distance between rows of borings, it beingsufficient to do the burning in only the first half of that distance toobtain the hydrocarbons of that entire section up to the next row ofborings by partial vaporzation, without any further expenditure ofenergy. The energy addition from the burnt-out rock is supported andincreased by the hot gases of combustion which were produced in theburning front but which without forming a gaseous phase became dissolved4in the liquid stratum contents and heated up the latter. 'If the heatenergy of a burning front which is advanced over only half the distancebetween two rows of borings is sufficient to obtain the hydrocarbonsbetween such rows, then the total amount of oxygen needed per m.3 of thedeposit will be diminished to Nm. This amount includes a slightly higheroxygen requirement for the building up of a burning zone between thetreatment borings and the leading borings. This amount will change byi10% if the specific gravity of the mineral oil is above or below theassumed value of 0.91 kg./l. and the pore volume of the rock in thestratum remains within the above-mentioned limits.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to Various usages andconditions. Consequently, such changes and modifications are properly,equitably, and intended to be, within the full range of equivalence ofthe following claims.

What is claimed is:

1. A method for the recovery of residual oil from underground petroleumdeposits by flooding and in situ combustion comprising the followingsteps:

(a) locating in a petroleum deposit at least one row of floodingboreholes connecting a structurally deep zone of said deposit, at leastone row of recovery boreholes connecting a structurally high zone ofsaid deposit, and at least one row of tre-ating boreholes and leadingboreholes, said treating and leading boreholes pdsitioned between saidflooding and recovering boreholes and connecting an intermediate zone ofsaid deposit;

(b) introducing under pressure into `said treating boreholes a limitedamount of activated combustion g-as having an increased oxygen contentfor achieving moderate combustion temperatures and igniting saidactivated combustion gas in said deposit between said treating boreholesand said leading boreholes whereby there is produced in the reactionzone a burning zone in which in situ combustion is performed in thestratum contents which have been extensively changed by the hot vaporsand gases;

(c) introducing flood water into said flooding boreholes under pressurewhereby a primary direction of flow of the stratum contents isestablished in said deposit between said flooding boreholes and saidrecovery boreholes whereby the axis of the re-action front between thetreating boreholes and the leading boreholes is shifted in parallelismin the direction toward the recovery boreholes, further conducting theflood water first through the burnt-out rock while being heated and thenthrough the reaction Zone while being further heated and vaporized, andconducting the resulting vapors through the burning front, burning andgasifying in the burning front, by said activated gases of combustionwith increased oxygen content, of the stratum contents which have beenstrongly altered by contact with said vapors, whereby from the-activated oxygen-containing gases of combustion a modified gas ofcombustion is formed, further conducting the steam which during pass-ageinto the reaction zone has become further heated so that at greaterdistances from the burning zone it will cause further flash vaporzationof the stratum contents in the primary ilow direction and so that thehot gases and vapors of the modified gases of combustion from theburning front will produce a delayed coking in the stratum contentswhich have already been ashed, so that forthe trailing burning frontthere will remain only a strongly altered stratum contents; and

(d) condensation and dissolving in the colder portions of the stratum ofthe modified combustion gases and vapors which are caused by thepressure gradient in the primary flow direction to flow toward therecovery boreholes while warming that portion of the stratum.

2. The method of claim 1, in which salt-containing flood water isintroduced into said treating boreholes and circulated between thelatter and said lead-ing boreholes between steps (c) and (d) of claim 1.

3. The method of claim 1, in which, after step (c), a pressure gradientis established between the flooding boreholes and the recovery boreholesand the migration Velocity of the burning zone is controlled by varyingthe amount of oxygen that is introduced into the combustion gas, so thatduring the combined flash vaporzation and delayed coking of the stratumcontents, by diminishing the amount of oxygen, larger portions of thestratum contents will remain behind as combustible materials whichretard the rate of burning, and conversely by increasing the amount ofoxygen smaller portions of the stratum contents will remain behind -ascombustible materials which strongly incre-ase the rate of burning.

`4. The method of claim 1, in which several rows of said treating andleading boreholes which are simulta- :ously tre-ated as in claim 1 step(c) are separated from 1e another by intermediate rows of tre-ating andleading Jreholes which at the beginning are only under the inlence ofthe pressure gradient and whose treatment under aim 1 step (c) does notbegin until after the burning )nes which are formed by thefirst-mentioned rows of eating and leading boreholes are driven backabout half ie distance to the nearest row of boreholes.

5. The method of claim 4, wherein at least a second )w of treating andleading boreholes is located perpenicular to said primary direction ofrecovery of the deposit ontents, the introduction of combustion gasesinto the rst row'of treating and leading boreholes being disconnued whensaid reaction zone is advanced approximately alf way between the firstand second row of treating and :ading boreholes and flood watercontaining dissolved xygen under pressure is introduced into said firstrow of reating and leading boreholes whereby the following iiood lateris heated by said hot burnt-out rock, oil residues in he burnt-out rockare burned by the dissolved oxygen and he oil-water contact line isadvanced to said second row lf tre-ating land leading boreholes whilethe temperature evel is maintained.

6. The method of claim 1, wherein certain of the fioodng boreholes aretemporarily closed while varying tmounts of flood Water are moved intocirculation through tdjacent flooding boreholes.

7. The method of claim 6, wherein treating and leadng boreholes whichare no longer used as such, are now 1sed as flooding boreholes in thesame manner as the floodng boreholes of claim 6.

`8. A method for the recovery of residual oil from inderground petroleumdeposits by flooding and in situ :ombustion comprising the followingsteps:

(a) locating in a petroleum deposit at least one row of floodingboreholes connecting a structurally deep zone of said deposit, at lea-stone row of recovery boreholes connecting a structurally high zone ofsaid deposit, and at least one row of treating boreholes and leadingboreholes, said treating and leading boreholes positioned between saidilooding and recovery boreholes and connecting an intermediate zone ofthe deposit;

(b) introducing under pressure into said treating boreholes a limitedamount of activated combustion gas having an increased oxygen contentfor achieving moderate combustion temperatures and igniting saidactivated combustion gas in said deposit between said treating boreholesand said leading boreholes whereby there is produced in the reactionzone a burning zone in which in situ combustion is performed in thestratum contents which have been extensively changed by the hot vaporsand gases;

(c) introducing ood water into said flooding boreholes under pressurewhereby a primary direction of flow of the stratum contents isestablished in said deposit between said flooding boreholes and saidrecovery boreholes whereby the -axis of the reaction front between thetreating boreholes and the leading boreholes is shifted in parallelismin the direction toward the recovery boreholes, further conducting theood water first through the burnt-out rock while being heated and thenthrough the reaction zone while being further heated and vaporized, andconducting the resulting vapors through the burning front, burning andgasifying in the burning front, by said acti- 12 vated gases ofcombustion with increased oxygen content, of the stratum contents whichhave been strongly altered by contact with said vapors, whereby from theactivated oxygen-containing gases of combustion a modified gas ofcombustion is formed, further conducting the steam which during passageinto the reaction zone has become further heated so that at greaterdistances from the burning zone it will cause further flash vaporizationof the stratum contents in the primary flow direction and so that thehot gases and vapors of the modified gases of combustion from theburning front will product a delayed coking in the stratum contentswhich have already been flashed, so that for the trailing burning frontthere will remain only a strongly altered stratum contents; and (d)delivering from the leading boreholes or from the recovery boreholes oflight gaseous hydrocarbons and other combustible gases during anadvanced stage of the process.

9. The method of claim 1, in which the combustion gas of step (b) isforced alternately into said treatment boreholes or into said leadingboreholes while the other one of these boreholes is closed, whereby aconical displacement of the region of activity of the activatedcombustion gas is effected by the pressure gradient that exists betweenthe treating boreholes and the leading boreholes, which results in anintensied activity of the conical displacement where the activatedcombustion gas enters the stratum, while at the same time the steamwhich is pro-l duced by contact of the flooding water with the burnt-outstone, mixed with activated combustion gas by the conical displacementin the direction of the closed borehole, is crowded out to such anextent that it will cause flash vaporization of the stratum contents,and where on the side toward the open borehole the activated gas ofcombustion which occurs there will cause a delayed coking in the greatlychanged stratum contents immediately ahead.

10. The method of claim 9, wherein the borehole not in use in opened,and prior to compressing said activated combustion gas, hydrocarbonswith modified combustion gas are temporarily introduced into thetreatment zone.

11. The method of claim 1, wherein only one re-action zone is initiallybuilt up, the reaction zone is then discontinued, and a flooding fromflooding boreholes is initiated at angles varying with respect to theaxis of said reaction zone previously built up, thereby transmitting theheat energy stored in the reaction zone in a direction toward the nextrow of borings.

12. The method of claim 1 wherein compressed air and flood water areintroduced into said ooding boreholes near the end of the productionperiod of the petroleum deposits.

References Cited by the Examiner UNITED STATES PATENTS 2,734,578 2/1956Walter 166-11 2,839,141 6/1958 Walter l66l1 2,841,375 7/1958 Salomonsson166--11 X 2,969,226 1/1961 Huntington 166-11 X 3,150,715 9/1964 Dietz166--11 X 3,153,448 10/1964 Dew et al. 166-11 X 3,196,945 7/1965 Craiget al. 166--11 CHARLES E. OCONNELL, Primary Examiner.

STEPHEN J. NOVOSAD, Examiner,

1. A METHOD FOR THE RECOVERY OF RESIDUAL OIL FROM UNDERGROUND PETROLEUMDEPOSITS BY FLOODING AND IN INSTU COMBUSTION COMPRISING THE FOLLOWINGSTEPS: (A) LOCATING IN A PETROLEUM DEPOSIT AT LEAST ONE ROW OF FLOODINGBOREHOLES CONNECTING A STRUCTURALLY DEEP ZONE OF SAID DEPOSIT, AT LEASTONE ROW OF RECOVERY BOREHOLES CONNECTING A STRUCTURALLY HIGH ZONE OFSAID DEPOSIT, AND AT LEAST ONE ROW OF TREATING BOREHOLES AND LEADINGBOREHOLES, SAID TREATING AND LEADING BOREHOLES POSITIONED BETWEEN SAIDFLOODING AND RECOVERING BOREHOLES AND CONNECTING AN INTERMEDIATE ZONE OFSAID DEPOSIT; (B) INTRODUCTING UNDER PRESSURE INTO SAID TREATINGBOREHOLES A LIMITED AMOUNT OF ACTIVATED COMBUSTION GAS HAVING ANINCREASED OXYGEN CONTENT FOR ACHIEVING MODERATE COMBUSTION TEMPERATURESAND IGNITING SAID ACTIVATED COMBUSTION GAS IN SAID DEPOSIT BETWEEN SAIDTREATING BOREHOLES AND SAID LEADING BORE HOLES WHEREBY THERE IS PRODUCEDIN THE REACTION ZONE A BURNING ZONE IN WHICH IN SITU COMBUSTION ISPERFORMED IN THE STRATUM CONTENTS WHICH HAVE BEEN EXTENSIVELY CHANGED BYTHE HOT VAPORS AND GASES; (C) INTRODUCING FLOOD WATER INTO SAID DEPOSITUNDER PRESSURE WHEREBY A PRIMARY DIRECTION OF FLOW OF THE STRATUMCONTENTS IS ESTABLISHED IN SAID DEPOSIT BETWEEN SAID FLOODING BOREHOLESAND SAID RECOVERY BOREHOLES WHEREBY THE AXIS OF THE REACTION FRONTBETWEEN THE TREATING BOREHOLES AND THE LEADING BOREHOLES IS SHIFTED INPARALLELISM IN THE DIRECTION TOWARD